Sandbox JA

Pathogenesis

Infection by L. monocytogenes causes the disease listeriosis.

An early study suggeseted that L. monocytogenes was unique among Gram-positive bacteria in that it possessed lipopolysaccharide, which served as an endotoxin. A later study did not support these findings.

The infective dose of L. monocytogenes varies with the strain and with the susceptibility of the victim. From cases contracted through raw or supposedly pasteurized milk, one may safely assume that in susceptible persons, fewer than 1,000 total organisms may cause disease. L. monocytogenes may invade the gastrointestinal epithelium. Once the bacterium enters the host's monocytes, macrophages, or polymorphonuclear leukocytes, it becomes blood-borne (septicemic) and can grow. Its presence intracellularly in phagocytic cells also permits access to the brain and probably transplacental migration to the fetus in pregnant women. The pathogenesis of L. monocytogenes centers on its ability to survive and multiply in phagocytic host cells.

Treatment

When listeric meningitis occurs, the overall mortality may reach 70%; from septicemia 50%, from perinatal/neonatal infections greater than 80%. In infections during pregnancy, the mother usually survives. Reports of successful treatment with parenteral penicillin or ampicillin exist. Trimethoprim-sulfamethoxazole has been shown effective in patients allergic to penicillin.

Bacteriophage treatments have been developed by several companies. EBI Food Safety and Intralytix both have products suitable for treatment of the bacteria. The FDA of the United States approved a cocktail of six bacteriophages from Intralytix, and a one type phage product from EBI Food Safety designed to kill the bacteria L. monocytogenes. Uses would potentially include spraying it on fruits and ready-to-eat meat such as sliced ham and turkey.

Gene Therapy

L. monocytogenes has been used in studies to deliver genes in vitro. However transfection efficiency remains poor.

Table

Disease	Findings
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